Centrifugal switch

ABSTRACT

A freely suspended prestressed spring is employed in conjunction with a pair of inertial masses to sense rotational velocity by means of centrifugal force. The switch is so mounted that the center of rotation of the spring-mass combination is located midway between the inertial masses, which move in opposite directions when the switch reaches a rotational velocity in excess of a threshold value. This movement causes an expansion of the tension spring which, in the absence of such overcoming force, pulls the masses toward one another. The inertial masses and prestressed spring are of electrically conducting material to electrically connect a pair of switch terminals contacted by the masses when a predetermined rotational velocity is reached.

United States Patent Primary Examiner-Robert K. Schaefer Assistant Examiner-William J. Smith Attorney--Ostrolenk, Faber, Gerb & Sofl'en ABSTRACT: A freely suspended prestressed spring is employed in conjunction with a pair of inertial masses to sense rotational velocity by means of centrifugal force. The switch is so mounted that the center of rotation of the spring-mass combination is located midway between the inertial masses, which move in opposite directions when the switch reaches a rotational velocity in excess of a threshold value. This movement causes an expansion of the tension spring which, in the absence of such overcoming force, pulls the masses toward one another. The inertial masses and prestressed spring are of electrically conducting material to electrically connect a pair of switch terminals contacted by the masses when a predetermined rotational velocity is reached.

[72] Inventor Joseph Baumoel Jericho, L.l., N.Y. [21] Appl. No. 24,487 [22] Filed Apr. 1, 1970 [45] Patented Jan. 4, 1972 [73] Assignee Controlotron Corporation Farmingdale, L. 1., N.Y.

[54] CENTRIFUGAL SWITCH 6 Claims, 1 Drawing Fig.

[52] 0.8. CI. 200/80 R, 73/535 [51] Int. Cl. 1101b 35/10 [50] Field of Search 200/80, 61.46; 73/535, 518, 545, 539, 540;102/70.2, 79

[56] References Cited UNITED STATES PATENTS 1,485,197 2/1924 OKeefe 102/702 380,824 4/1888 Schlepegrell 102/702 2,657,035 10/1953 Hartman 200/80 R X 2,712,791 7/1955 Bleakney et a1. 102/79 X PATENTEDJAN 4m 3.632.922

IN VENTOR. JOJ'E/f/ 5/70/ 406! CENTRIFUGAL SWITCH This invention relates to a centrifugal switch and, more particularly, to such a device which provides contact closure when a structure on which it is mounted is rotated at a predetermined velocity.

As will become clear hereinafter, the switch employs a freely suspended prestressed tension spring in conjunction with a pair of inertial masses to sense rotational velocity by means of centrifugal force applied to the two masses. The switch is so mounted that the center of its rotation is located midway between the inertial masses, which move away from one another when the switch is rotated at a velocity in excess of a threshold value. This movement tends to expand the tension spring which, for velocities below the rotational threshold, overcomes any centrifugal force to pull the masses toward one another. By selecting the prestressed spring and inertial masses to be of electrically conducting material, an electrical connection can be established between a pair of switch terminals arranged to be contacted by the two masses when a predetermined rotational velocity has been reached. Subsequent operation of electrical apparatus coupled to respective ones of the contact terminals provides an indication that the predetermined rotational speed has, in fact, been reached.

This will be more fully understood from a consideration of the following description, taken in connection with the single F IGURE of the drawing which shows one embodiment of the centrifugal switch of the invention in partially sectional view.

As illustrated, the switch assembly is of a generally tubular construction, having a cylindrical casing fabricated from a polycarbonate plastic, for example. A pair of inertial masses 12, 14 are also shown, and are dimensioned for positioning within an internal chamber 16 of the case 10. More particularly, the chamber 16 has enlarged outer portions 18, 20 and a connecting inner portion 22. As will be noted, the diameter of the inertial masses 12, 14 is selected so the two masses may fit within the outer chamber portions 18, 20 in a manner to permit relatively free movement therein without impairment by the upper and lower chamber walls. As will also be noted, the facing ends of the masses l2, 14 are so configured that banked walls of the inner chamber portion 22 serve as a stop to unrestrained movement of the masses toward one another.

A tension spring 24 of prestressed electrically conductive material is also shown in the drawing. One end of this spring 26 is latched by a projection 28 on the inertial mass 12 (to be held thereby) while the other end of the spring 30 is attached by a corresponding projection 32 on the inertial mass 14 (for similar retention). The restoring force of the prestressed spring 24 is so selected that in the static condition, (i.e., with zero rotational velocity of the structure on which the switch is mounted) the masses 12, 14 are pulled towards one another sufficiently to bear against the banked walls of the inner chamber portion 22.

A pair of end caps 32, 34 also of electrically conductive material, are shown positioned at the opposite ends of the casing 10 and including an electrical contact terminal, 36 in one instance and 38 in the other. As will become clear hereinafter, the rotational velocity of the structure at which closure of these switch terminals will occur can be varied by means of a pair of adjustable screws 40, 42 which (by means of a screwdriver or similar such instrument) can control advance or withdrawal of the contact terminals into the outer chamber portions 18, 20. Electrical leads 44, 46 are lastly illustrated in the drawing as being in contact with the end caps 32, 34, and provide connection of the switch to appropriate apparatus, the operation of which gives an indication whether or not a particular rotational velocity has been reached. As will be appreciated, this corresponds to a closed or open switch position, respectively, and operates to complete or incomplete an electrical circuit.

in one embodiment of the invention, the adjustable screw units 40, 42 were selected to be of stainless steel composition. The end caps 32, 34 were likewise selected of brass while the leads 44, 46 were copper tinned for effective transfer of electrical energy. When the switch rotational was to be used in environments where velocities of L000 r.p.m. or so were in order, the inertial masses 12, 14 were selected of brass. Where higher rotational velocities of the order of 10,000 r.p.m. were expected, the inertial masses l2, 14 were selected instead to be an aluminum alloy. Conversely, where lower rotational speeds were envisioned, inertial masses of tungsten were employed. Both the inertial masses 12, 14 and the contact terminals 36, 38 were plated with precious metals in all of these environments, with the terminals 36, 38 and the tension spring 24 being of a stainless steel composition. Where extremely high accuracy was required, the stainless steel tension spring 24 was replaced by a spring of Ni-Span-C material.

A centrifugal switch of 1%inch length was thus fabricated and designed to close at a rotational velocity of 1,000 r.p.m. I50 r.p.m., with a stainless steel tension spring 24 and brass inertial masses 12, 14. The diameter of the cylindrical casing 10 was three-eighths of an inch, with lead length for the units 44, 46 being of the order of three-fourth of an inch. Also, to facilitate location of the center of rotation of the switch, a locating notch 48 was cut into the casing midway between the masses 12, 14.

in operation-and until a threshold value of rotational velocity is reached-the tension spring 24 of the assembly thus described causes the two masses l2, 14'to bear against the banked walls of the inner casing chamber portion 22. As the structure on which the switch is mounted undergoes an increased rotational velocity beyond the threshold, the centrifugal forces acting on the two masses l2, 14 increase to cause the spring 24 to expand and to move the masses 12, 14 away from one another towards their respective contact terminals 36, 38. As the velocity continues to increase still further, increased centrifugal forces are applied to the inertial masses 12, 14 and, eventually expands the spring 24 to the point where the two masses 12, 14 contact the terminals 36, 38. Since the spring 24 and the masses 12, 14 are of metallic composition, electrical contact will eventually be achieved and electrical connection established between terminals 36 and 38. The operation of electrical apparatus coupled to the leads 44, 46 then provides an indication that the rotational speed at which contact will occur has been reached.

By varying the restoring force of spring 24, the size of the inertial masses 12, 14 and the distance between the inertial mass and its associated electrical contact at steady state, a wide range of controls can be exerted on the actual rotational velocity necessary to achieve contact closure. Alternatively, adjustment of the screws 40, 42 can serve as an additional means of controlling the rotational velocity to which the structure must be put before switch closure occurs.

One advantage of the centrifugal switch of the present invention is its extreme simplicity. A second advantage is that its contact closure is substantially independent of linear acceleration. In the event a linear acceleration is experienced, it will thus be seen that one inertial mass will be forced toward its contact terminal, but the second inertial mass will be forced away from its contact tenninal toward its banking wall of the inner casing chamber portion.

Furthermore, by having the inertial masses joined by a freely suspended spring, false contact closures can be substantially avoided under conditions of vibration during rotational velocities just below that necessary to cause contact closure. That is, any vibration having a tendency to move one mass towards its contact closure will have a similar directional effect on the other inertial mass through the spring so that both masses move in the same direction. As in the case of linear acceleration, the result is that completion of the electrical circuit is prevented as the two masses do not both move towards their respective contact terminals.

A further feature of the above construction resides in the fact that the inertial masses are prevented from moving by the spring-restoring force until the rotational velocity reaches the threshold value. in this respect, the two masses cannot absorb kinetic energy below this threshold, which might otherwise cause random contact as the masses vibrate.

In constructing a centrifugal switch as above described it has been found advantageous to heat seal the plastic housing so as to prevent the entry of moisture or contamination into the switch area. Metal enclosures which are hermetically sealed can also be used, simply by incorporating an insulating collar against which the masses could be banked. Also, instead of using axial leads to connect to the contact terminals of the unit, it will be noted that solder terminals or right-angle printed circuit mounting terminals may be employed at either end. Such arrangements are positioned external to the centrifugal switch itself and are possible constructions regardless of the compositions of the cooperating materials selected according to desired features of closure.

Although there has been described a preferred embodiment of this novel invention, many variations and modifications will be apparent to those skilled in the art. Therefore, this invention is to be limited, not by the specific disclosure herein, but only by the appended claims.

l claim:

1. A compact centrifugal switch comprising;

a pair of inertial masses situated in spaced-apart relation within a common plane, with each said mass having a front and back surface whereby a gap is provided between said front surfaces;

a tension spring spanning said gap for joining thefront surfaces of said inertial masses and exhibiting a restoring force tending to pull said masses toward one another, said spring being completely isolated and spaced from all other elements of said switch;

and first and second terminal means respectively positioned adjacent to the back surfaces of said inertial masses;

with said inertial masses, tension spring and terminal means being of electrically conducting composition to complete electrical connection between said terminal means through said spring and inertial masses when a structure to which said switch is secured is subjected to a rotational velocity impressing sufficient centrifugal forces on said inertial masses in excess of said spring-restoring force to effect movement of said masses away from one another toward establishing electrical contact with said terminal means by way of the back surfaces of said masses.

2. The switch of claim 1 wherein said inertial masses, tension spring and terminal means are included within a casing having first and second outer chamber portion within which said inertial masses are positioned and a connecting inner chamber portion within which said compression spring is positioned for joining said facing front surfaces of said masses.

3. The switch of claim 2 wherein the front surfaces of said masses are so dimensioned with respect to said inner casing chamber portion that the walls of said portion limit the movement of said inertial masses toward one another under control of the restoring force of said tension spring.

4. The switch of claim 3 wherein there is also included first and second control means respectively associated with said first and second terminal means to adjust the adjacent positioning of said means with respect to the back surfaces of said inertial masses.

5. The switch of claim 4 wherein the rotational velocity which impresses sufficient centrifugal forces on said inertial masses to effect electrical contact between said switch terminals is controllable by selection of the dimensions for said inertial masses, restoring force of said tension spring and adjustment of said control means to vary the distance between said tenninal means and the back surface of said inertial masses in the absence of rotational velocity.

6. The switch of claim 5 wherein the dimensions of said inertial masses, restoring force of said tension spring and adjustment of said control means are so selected that movement of said inertial masses away from one another toward establishing electrical contact is inhibited until the rotational velocity of the structure to which said switch is secured approaching the rotational velocity at which electrical contact with said switch terminals to complete electrical connection therebetween actually occurs.

I! k k I 

1. A compact centrifugal switch comprising: a pair of inertial masses situated in spaced-apart relation within a common plane, with each said mass having a front and back surface whereby a gap is provided between said front surfaces; a tension spring spanning said gap for joining the front surfaces of said inertial masses and exhibiting a restoring force tending to pull said masses toward one another, said spring being completely isolated and spaced from all other elements of said switch; and first and second terminal means respectively positioned adjacent to the back surfaces of said inertial masses; with said inertial masses, tension spring and terminal means being of electrically conducting composition to complete electrical connection betWeen said terminal means through said spring and inertial masses when a structure to which said switch is secured is subjected to a rotational velocity impressing sufficient centrifugal forces on said inertial masses in excess of said spring-restoring force to effect movement of said masses away from one another toward establishing electrical contact with said terminal means by way of the back surfaces of said masses.
 2. The switch of claim 1 wherein said inertial masses, tension spring and terminal means are included within a casing having first and second outer chamber portion within which said inertial masses are positioned and a connecting inner chamber portion within which said compression spring is positioned for joining said facing front surfaces of said masses.
 3. The switch of claim 2 wherein the front surfaces of said masses are so dimensioned with respect to said inner casing chamber portion that the walls of said portion limit the movement of said inertial masses toward one another under control of the restoring force of said tension spring.
 4. The switch of claim 3 wherein there is also included first and second control means respectively associated with said first and second terminal means to adjust the adjacent positioning of said means with respect to the back surfaces of said inertial masses.
 5. The switch of claim 4 wherein the rotational velocity which impresses sufficient centrifugal forces on said inertial masses to effect electrical contact between said switch terminals is controllable by selection of the dimensions for said inertial masses, restoring force of said tension spring and adjustment of said control means to vary the distance between said terminal means and the back surface of said inertial masses in the absence of rotational velocity.
 6. The switch of claim 5 wherein the dimensions of said inertial masses, restoring force of said tension spring and adjustment of said control means are so selected that movement of said inertial masses away from one another toward establishing electrical contact is inhibited until the rotational velocity of the structure to which said switch is secured approaching the rotational velocity at which electrical contact with said switch terminals to complete electrical connection therebetween actually occurs. 